A lathe generally performs processing by abutting a tool such as a cutting tool being a cutter against a workpiece for machining which is rotationally driven by a main spindle.
Further, a lathe which performs a plurality of different kinds of processings, namely, combined processing on a workpiece is also in wide use, and various types of lathes or machine tools such as disclosed in, for example, Patent Documents 1 to 5 are known.
Patent Document 1: JP H11-138374 A
Patent Document 2: JP H10-15702 A
Patent Document 3: EP 1270145 A2
Patent Document 4: JP S62-236607 A
Patent Document 5: JP H7-227704 A
A combined processing lathe disclosed in Patent Document 1 is a lathe having a tool magazine holding a plurality of kinds of cutting tools mounted thereon, and capable of performing combined processing while successively changing the tool held by a tool spindle being a single spindle with the use of a tool changer in accordance with the processing contents. As a tool used in such a combined processing lathe, there are various types of tools such as “cutting tool (tool bit)” used for turning in which processing is performed without rotating the tool spindle, “drill” used by rotating the tool spindle, “milling cutter” which performs surface processing, and “grindstone tool” which performs grinding.
However, in such a combined processing lathe in which the tool held by the tool spindle being the single spindle is changed by the tool changer according to each processing content, although the flexibility regarding the number of tools and a processing method conducted by the combined processing lathe is high, since the tool has to be changed at every processing step in which a different tool is used, the time for changing tools, namely, an unprocessing time has to be provided, which brings a limitation to the reduction in the processing time per one workpiece.
In order to enable to change the tools in such a lathe in a short period of time, a flat turret and a rotary turret (turning tool post) are used in a multifunction lathe disclosed in, for example, Patent Document 2. The flat turret arranges a plurality of tools (cutters) linearly and in a comb-teeth shape, and by moving the tool post (tool bit) in the arranged direction, it can select either one of the tools attached to the tool post so as to correspond the tool to a workpiece for machining.
Meanwhile, the rotary turret arranges, on respective side surfaces of a rotatable turret having a polygonal column shape, each of tools (cutters) in a radial manner with respect to a rotary shaft, and by dividedly rotating the turret, it can select either one of the tools attached to the turret so as to correspond the tool to a workpiece for machining.
It is also conducted that the processing time is reduced by independently or simultaneously performing the processings with these two kinds of tool posts.
Since each the aforementioned flat turret and rotary turret can selectively attach the plurality of tools, if the plurality of tools used for the processings are attached to the respective turrets, there is no need to change the tools and the necessary tools can be selected in a short period of time, resulting that the processing time for the workpiece can be reduced.
Since the flat turret selects the tool by its linear movement, the selection speed thereof is fast, and when a tool used for an immediately preceding processing and a tool to be used for the following processing are adjacently attached, the tool to be used for the following processing can be selected in a quite short period of time. However, if the tools are attached separately in the vicinity of both end portions of the turret, there is a problem that a movement stroke becomes long and the selection time also becomes long.
Meanwhile, although it rather takes time for the rotary turret to dividedly rotate the turret, even if the tool used for the immediately preceding processing and the tool to be used for the following processing are attached in separate positions, by selecting the rotating direction, the difference in selection time does not become considerably large.
Accordingly, in a machine tool disclosed in, for instance, Patent Document 3, respective side surfaces of a tool post head corresponding to the turret are divided into a plurality of parts (hereinafter, referred to as “stage”) having intervals therebetween in a direction along a rotary shaft of the tool post head, each stage has a different kind of tool attached thereto, and the tool post head can be integrally and linearly moved in the direction along the rotary shaft.
Therefore, the tool post head can select, same as the rotary turret, the tool attached to the same stage on the side surface by being dividedly rotated (turned) around the rotary shaft, and can select, same as the flat turret, either of the plurality of tools attached to the different stage on the same side surface of the tool post head by linearly moving in the direction along the rotary shaft.
Specifically, the tool post with this structure has both functions of the rotary turret and the flat turret, and it can select, when the tool used for the immediately preceding processing and the tool to be used for the following processing are attached to the different stages on the same side surface of the tool post head, the tool to be used for the following processing in a quite short period of time only by linearly moving the tool post head in the direction of rotary shaft.
However, if the tool to be used for the following processing is attached to the different stage at the different dividedly rotated position of the tool post head, there is a need that the tool post head is dividedly rotated as well as moved linearly. Accordingly, the time for selecting the tool, namely, the unprocessing time has to be provided, resulting that the reduction in the processing time per one workpiece cannot be fully realized. Further, since disposition angles of the tools are decided depending on the number of divisions of the side surfaces of the tool post head in its rotational direction, there are a lot of restrictions on flexibility of processing in such a case where, for example, processing on a workpiece held by a first spindle and processing on a workpiece held by a second spindle are simultaneously conducted, and the tool post cannot be used effectively, which also results in creating a problem when reducing the processing time per one workpiece.
In addition, examples where a plurality of turrets are disposed in an automatic lathe while being shifted to the positions in a direction of rotary shaft thereof are also disclosed in Patent Documents 4 and 5. According to Patent Document 4, two turrets (rotary tables) are provided in which they can be independently rotated and one of them can be shifted in an axial direction with respect to the other one. Further, it is structured such that both the turrets are fixed, together with their cutters (tools), to fixed positions with respect to a housing during a cutting operation, and the respective turrets can be dividedly rotated independently during a change of cutters.
However, it is not possible to previously select, during when the processing is performed using the cutter (tool) of one of the turrets, a cutter (tool) to be used for the following processing by dividedly rotating the other turret.
Patent Document 5 discloses that the number of usable tools is increased without enlarging turrets, by integrating two turrets and disposing them in series in a state where they are shifted by predetermined angles in rotational directions thereof, and that rotating tools attached to either of the turrets can be rotated by one common driving shaft.
However, the turrets cannot be dividedly rotated separately and independently, so that also in this case, it is not possible to previously select, during when the processing is performed using the tool of one of the turrets, a tool to be used for the following processing by dividedly rotating the other turret.
Accordingly, each of these turrets cannot fully reduce the time taken for selecting the tools, namely, the unprocessing time, resulting that the reduction in the processing time per one workpiece cannot be fully realized. Further, there are a lot of restrictions on the flexibility of processing.